Introduction:
Calcification of the mitral valve (MV) annulus and leaflets is an
increasingly common cause of MV stenosis (MS).1,2Mitral annular calcification (MAC) has four principal pathophysiological
mechanisms: degeneration, atherosclerosis, increased MV stress, and
abnormal calcium phosphate metabolism.3 These
processes lead to dystrophic calcification, increased lipid
peroxidation, and chronic expression of transforming growth factor-β and
inflammatory cytokines that promote phenotypic trans-differentiation of
valvular interstitial cells into osteoblast-like
cells.3–5 These microscopic changes can eventually
cause the macroscopic changes seen with MAC, including a larger, flatter
annulus with reduced mitral annular dynamism throughout the cardiac
cycle.6 As the disease process continues, the
dystrophic calcification extends into the left ventricular (LV) inflow
tract and onto the MV leaflets, thereby obstructing LV inflow
(Figure 1 ).7 This disease process has
increasingly been recognized as degenerative MS (DMS)
Current guidelines for the management of patients with valvular heart
disease define severe MS with a mitral valve area (MVA) ≤ 1.5
cm2 independent of the etiology of MS. According to
the guidelines, severe stenosis usually corresponds to a mean
transmitral pressure gradient (TMPG) of 5 to 10 mmHg at normal heart
rates.8 It should be noted that these quantification
values have only been validated in patients with rheumatic MS (RMS) and
lack similar validation in DMS populations. The anatomic MVA of DMS can
be estimated with either electrocardiogram-gated multidetector cardiac
computed tomography or three-dimensional echocardiography, but their
availability is limited compared to that of two-dimensional
echocardiography. 6,9–11
Transthoracic echocardiography is widely available, but methods commonly
used for evaluating MS severity (i.e., planimetry, pressure
half-time, and color flow Doppler) have not been validated for DMS.
Planimetry is challenging due to difficulty with obtaining the correct
orientation of the image plane.11–13 The abnormal LV
compliance that frequently accompanies DMS decreases the accuracy of the
pressure-half time method and limits its
applicability.10 The applicability of color flow
Doppler to DMS is limited by the absence of flow contraction secondary
to the MV being distorted into a tubular morphology.10,11,14 Continuity equation method is usually limited
in DMS due to the frequent co-occurrence of mitral regurgitation (MR),
aortic regurgitation, or atrial fibrillation in this
population.6 There is ample evidence to support the
TMPG as a surrogate for stenosis severity in RMS, but it is affected by
changes in valve morphology and abnormal atrioventricular compliance as
well as volume overload conditions such as end-stage renal disease
(ESRD), and hence may not be appropriate for
DMS.11,14–16
The goals of this study were to compare echocardiographic
characteristics of DMS and RMS, identify echocardiographic variables
reflective of DMS stenosis severity, propose a dimensionless index of MS
(Dimensionless Mitral Stenosis Index, DMSI) to help with estimation of
DMS severity by transthoracic echocardiography, and examine the
prognostic determinants of all-cause mortality in patients with DMS.